The present invention relates in general to function generators, and more particularly to a function generator for generating digital data which represent a function of the time interval between events.
In various apparatus, it is desirable to produce a digital readout which represents a function of the time interval between two events. For example, it may be desirable to have a digital readout representing the frequency associated with periodic functions of the human body, such as heart beats, respiration and the like. Heretofore, digital readouts of frequency were difficult to obtain, because conventional digital frequency measurement required the accumulation of input events in a period of time. This period must be long, in the case of heart beats and other low frequency signals, if adequate resolution is to be obtained. Alternatively, period can be measured quickly, but it has to have a non-linear (1/x) relationship to frequency.
Heretofore, digital or analog computers were employed to enable the generation of a digital readout from a non-linear time related signal. Such computers were of considerable complexity and cost.
When the digital readout represents a function of the time interval between two events and the relationship is linear with respect to a time interval, the desired functional relationship may be expressed as a linear equation, i.e., N.sub.out =A.DELTA.T, where the N.sub.out is a digital readout; A is a coefficient of proportionality; and .DELTA.T is the elapsed time between events. In this instance, a relatively simple time interval counter will produce the digital readout. However, in those instances in which the function of time represented by F(t) is a non-linear function of time, i.e., 1/T, T.sup.2, N/T, et cetera, the apparatus for producing a digital readout has been unduly complex.